Dielectric Composition, Dielectric Element, Electronic Component and Laminated Electronic Component

ABSTRACT

A dielectric composition, a dielectric element, an electronic component and a laminated electronic component are disclosed. In an embodiment the dielectric composition includes particles having a perovskite crystal structure including at least Bi, Na, Sr and Ti, wherein the content of the at least one element selected from La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Yb, Ba, Ca, Mg or Zn is between 0.5 molar parts and 11.1 molar parts, taking the Ti content of the dielectric composition as 100 molar parts, wherein 0.17≤α≤2.83, where α is the molar ratio of Bi with respect to Sr in the dielectric composition, and wherein at least some of the particles include a high-Bi phase having a Bi concentration of at least 1.2 times the mean Bi concentration of the dielectric composition as a whole.

This patent application is a national phase filing under section 371 ofPCT/EP2016/063899, filed Jun. 16, 2016, which claims the priority ofJapanese patent application 2015-143389, filed Jul. 17, 2015, each ofwhich is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present invention relates to a dielectric composition and adielectric element comprising the same, and to an electronic componentand a laminated electronic component. More specifically, the presentinvention relates to a dielectric composition, a dielectric element, anelectronic component and a laminated electronic component which are usedfor applications with a relatively high rated voltage.

BACKGROUND

Recent years have seen increasing demand for miniaturization andincreased reliability of dielectric elements as electronic circuitsreach higher densities. Miniaturization of electronic components such aslaminated ceramic capacitors, together with increased capacity andhigher reliability are rapidly progressing, while the applications ofelectronic components such as laminated ceramic capacitors are alsoexpanding. Various characteristics are required as these applicationsexpand.

For example, there is a growing shift from silicon to silicon carbide insemiconductors used for circuits in AC-DC inverters and DC-DC convertersfor motor vehicles. There is a need for even greater reliability incapacitors used around silicon carbide semiconductors. Specifically,there is a need for a high dielectric constant when a high DC bias isapplied. Furthermore, there is also a need for a long high-temperatureload lifespan in order to increase the lifespan when a high voltage isapplied under a high temperature. In addition, there is simultaneously aneed for high mechanical strength in order to prevent cracking andsplintering etc. during production of the dielectric material andmounting on a substrate.

In order to respond to these requirements, dielectric compositionshaving barium titanate (BaTiO₃) as the main component are ofteninvestigated and used in general. However, there are problems withelectronic components which have dielectric layers comprising aconventional dielectric composition having BaTiO₃ as the main componentin that the dielectric constant decreases when a high DC bias isapplied. It is difficult to avoid this problem because BaTiO₃ is aferroelectric material. In addition, the higher the DC bias, the morethe dielectric constant tends to decrease. When such electroniccomponents are used for applications involving high DC bias applicationit is therefore necessary to anticipate the amount of reduction in thedielectric constant and to use a plurality of the electronic componentsconnected in parallel in order to maintain the required capacitance ordielectric constant. Methods for connecting a plurality of theelectronic components in parallel are a particular problem in terms ofhigh cost.

Furthermore, a laminated ceramic capacitor which has dielectric layerscomprising a conventional dielectric composition having BaTiO₃ as themain component has a relatively good high-temperature load lifespan.However, it is anticipated that the environments under which electroniccomponents are used will become even more harsh in the future so afurther improvement in the high-temperature load lifespan would bedesirable.

When a conventional dielectric composition having BaTiO₃ as the maincomponent is used for applications under a low DC bias of several voltsor less, the field intensity applied to the dielectric layers is small,so the thickness of the dielectric layers can be set to a sufficientlythin level that breakdown does not occur. It is therefore possible toreduce the size of the dielectric element. In addition, there are alsovery few cases in which cracking etc. becomes a problem because ofexternal stress or the like to which the electronic component issubjected during production of the dielectric material and mounting on asubstrate. However, for applications involving usage under a high DCbias of several hundred volts or greater, the dielectric layers must besufficiently thick to ensure safety. The dielectric material thereforetends to be larger and heavier for applications involving usage under ahigh DC bias. The mechanical strength required also increases as aresult. The dielectric material may crack or splinter if it is droppedduring production because it is not possible to ensure adequatemechanical strength which is commensurate with the size and weight ofthe dielectric material.

In order to solve these problems, Japanese Patent Application JP 2006206362 describes a dielectric porcelain having barium titanate as themain component and containing Ca, Sr, Mg, Mn and rare earth elements,and characterized by a core-shell structure in which the Caconcentration is greater at the particle surface than at the centre ofthe particle, and the Sr, Mg, Mn and rare earth elements are unevenlydistributed at the particle surface.

Furthermore, Japanese Patent Application JP 2005 22891 describes adielectric porcelain comprising both perovskite barium titanate crystalgrains in which part of the B site is substituted with Zr (BTZ-typecrystal grains), and perovskite bismuth sodium titanate crystal grainsin which part of the A-site is substituted with Sr (BNST-type crystalgrains). That dielectric porcelain is characterized by a core-shellstructure in which Mg, Mn and at least one rare earth element arepresent in the grain boundary phase between the BTZ-type crystal grainsand the BNST-type crystal grains, and the mean particle size of both theBTZ-type crystal grains and the BNST-type crystal grains is 0.3-1.0 μm.

Dielectric porcelain comprising BaTiO₃ as the main component and havinga core-shell structure such as that described in Japanese PatentApplication JP 2006 206362 has a relatively high dielectric constantvalue of 2500 or greater at 20° C. when a DC bias is not applied.However, a sufficiently good value is not exhibited for the rate ofchange in the dielectric constant or the rate of change in capacitancewhen a DC bias of 5 V/μm is applied. Furthermore, a sufficiently goodvalue is not exhibited for the high-temperature load lifespan. Inaddition, there is no mention of the mechanical strength.

On the other hand, the ceramic composition described in Japanese PatentApplication JP 2005 22891 has a relatively high dielectric constant whena DC bias is not applied, and the DC bias characteristics when a DC biasof 3 V/μm is applied are also less than −20%. However, the value cannotbe considered sufficient for use under a high voltage, such as in aDC-DC converter or AC-DC inverter for a motor vehicle. Furthermore,there is no mention of the high-temperature load lifespan or mechanicalstrength.

SUMMARY OF THE INVENTION

Embodiments provide a dielectric composition which can be used inlocations where a high voltage is applied and for applications with arelatively high rated voltage, which has a good dielectric constant whena DC bias is applied and good DC bias characteristics, and which alsohas a good high-temperature load lifespan and good mechanical strength.Further embodiments provide a dielectric element comprising thedielectric composition, an electronic component and a laminatedelectronic component.

In various embodiments the dielectric composition comprises particleshaving a perovskite crystal structure including at least Bi, Na, Sr andTi, wherein the dielectric composition includes at least one selectedfrom among La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Yb, Ba, Ca, Mg andZn, wherein the content of the at least one selected from among La, Ce,Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Yb, Ba, Ca, Mg and Zn is between 0.5molar parts and 11.1 molar parts, taking the Ti content of thedielectric composition as 100 molar parts, wherein 0.17≤α≤2.83, where αis the molar ratio of Bi with respect to Sr in the dielectriccomposition, wherein at least some of the particles include a high-Biphase having a Bi concentration of at least 1.2 times the mean Biconcentration of the dielectric composition as a whole, and wherein thetotal surface area of the high-Bi phase within the particles in thecross section of the dielectric composition is between 0.1% and 15% ofthe total surface area of the particles.

The dielectric composition according to embodiments of the presentinvention has the constitution described above, and as a result thedielectric constant when a DC bias is applied and the DC biascharacteristics are improved, and the high-temperature load lifespan andmechanical strength are also improved at the same time.

The dielectric composition according to embodiments of the presentinvention is such that the total content of Bi included in the high-Biphase within the particles is, as an atomic ratio, between 1.15 and 2.15times the total content of Bi included in the portion within theparticles outside the high-Bi phase. By virtue of this feature, thedielectric constant when a DC bias is applied, the DC biascharacteristics, the high-temperature load lifespan and/or themechanical strength are further improved.

A dielectric element according to embodiments of the present inventionis provided with the abovementioned dielectric composition.

An electronic component according to embodiments of the presentinvention is provided with a dielectric layer comprising theabovementioned dielectric composition.

A laminated electronic component according to embodiments of the presentinvention has a laminated portion formed by alternately laminating aninternal electrode layer and a dielectric layer comprising theabovementioned dielectric composition.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a ceramic capacitor according to anembodiment of the present invention;

FIG. 2 is a view in cross section of a laminated ceramic capacitoraccording to a further embodiment of the present invention; and

FIG. 3 is a schematic diagram of particles in a dielectric compositionaccording to another embodiment of the present invention.

Embodiments of the present invention will be described below withreference to the figures. It should be noted that the present inventionis not limited to the following embodiments. Furthermore, theconstituent elements described below include elements which can bereadily envisaged by a person skilled in the art and also elements whichare substantially the same. In addition, the constituent elementsdescribed below may be combined, as appropriate.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

FIG. 1 is a schematic diagram of a ceramic capacitor according to anembodiment of the present invention.

As shown in FIG. 1, a ceramic capacitor 100 according to an embodimentof the present invention comprises a disc-shaped dielectric body 1 and apair of electrodes 2, 3. The single-layer ceramic capacitor 100 isobtained by forming the electrodes 2, 3 on both surfaces of thedielectric body 1. There is no particular limitation as to the shapes ofthe dielectric body 1 and the electrodes 2, 3. Furthermore, there is noparticular limitation as to the dimensions thereof either, and suitabledimensions should be set in accordance with the application.

The dielectric body 1 comprises a dielectric composition according tothis embodiment. There is no particular limitation as to the material ofthe electrodes 2, 3. For example, Ag, Au, Cu, Pt, Ni or the like may beused, but other metals may also be used.

FIG. 2 is a schematic cross-sectional diagram of a laminated ceramiccapacitor according to a different embodiment of the present invention.

As shown in FIG. 2, a laminated ceramic capacitor 200 according to adifferent embodiment of the present invention comprises a capacitorelement main body 5 having a structure in which dielectric layers 7 andinternal electrode layers 6A, 6B are alternately stacked. A pair ofterminal electrodes 11A, 11B which conduct, respectively, with theinternal electrode layers 6A, 6B alternately arranged inside the elementmain body 5 are formed at both ends of the element main body 5. There isno particular limitation as to the shape of the element main body 5, butit is normally a cuboid shape. Furthermore, there is no particularlimitation as to the dimensions thereof, and suitable dimensions shouldbe set in accordance with the application.

The internal electrode layers 6A, 6B are provided in such a way as to beparallel. The internal electrode layers 6A are formed in such a way thatone end thereof is exposed at the end surface of the laminated body 5where the terminal electrode 11A is formed. Furthermore, the internalelectrode layers 6B are formed in such a way that one end thereof isexposed at the end surface of the laminated body 5 where the terminalelectrode 11B is formed. In addition, the internal electrode layers 6Aand internal electrode layers 6B are disposed in such a way that themajority thereof is overlapping in the direction of stacking.

There is no particular limitation as to the material of the internalelectrode layers 6A, 6B. For example, a metal such as Au, Pt, Ag, Ag—Pdalloy, Cu or Ni etc. may be used, but it is also possible to use othermetals.

The terminal electrodes 11A, 11B are provided at the end surfaces of thelaminated body 5 in contact with the ends of the internal electrodelayers 6A, 6B which are exposed at said end surfaces. By virtue of thisstructure, the terminal electrodes 11A, 11B are electrically connectedto the internal electrode layers 6A, 6B, respectively. The terminalelectrodes 11A, 11B may comprise a conductive material having Ag, Au, Cuor the like as the main component thereof. There is no particularlimitation as to the thickness of the terminal electrodes 11A, 11B. Thethickness thereof is appropriately set in accordance with theapplication and the size of the laminated dielectric element, amongother things. The thickness of the terminal electrodes 11A, 11B may beset at 10-50 μm, for example.

The dielectric layers 7 comprise the dielectric composition according tothis embodiment. The thickness of each dielectric layer 7 may be freelyset and there is no particular limitation. The thickness may be set at1-100 μm, for example.

Here, the dielectric composition according to this embodiment has aperovskite crystal structure containing at least Bi, Na, Sr and Ti, andcomprises at least one selected from among La, Ce, Pr, Nd, Sm, Eu, Gd,Tb, Dy, Ho, Yb, Ba, Ca, Mg and Zn (also referred to below as an“auxiliary component”).

The dielectric composition having a perovskite crystal structure is apolycrystalline material comprising, as the main phase, a perovskitecompound represented by the general formula ABO₃, where A includes atleast one selected from Bi, Na and Sr, and B includes at least Ti.

If the whole of A is taken as 100 at. %, the proportion of Bi, Na, Srcontained in A is preferably a total of at least 80 at. %. Furthermore,if the whole of B is taken as 100 at. %, the proportion of Ti containedin B is preferably at least 80 at. %.

Furthermore, a dielectric composition 300 according to this embodimentis preferably such that 0.17≤α≤2.83, where α is the molar ratio of Biwith respect to Sr in the dielectric composition. If a is excessivelysmall, there tends to be a deterioration in the dielectric constant. Ifa is excessively large, there tends to be a deterioration in one or moreof the dielectric constant when a DC bias is applied, the DC biascharacteristics, the high-temperature load lifespan, and the mechanicalstrength.

In addition, the dielectric composition 300 contains between 0.5 molarparts and 11.1 molar parts of the auxiliary component, where the Ticontent of the dielectric composition is taken as 100 molar parts. Ifthe auxiliary component content is excessively small, the mean particlesize which will be described later tends to be excessively large andthere tends to be a deterioration in the DC bias characteristics whichwill be described later. If the auxiliary component content isexcessively large, there tends to be a reduction in the dielectricconstant.

FIG. 3 is a schematic diagram showing particles (sintered particles) ofthe dielectric composition 300 forming the dielectric body 1 of thesingle-layer ceramic capacitor 100 and the dielectric layers 7 of thelaminated ceramic capacitor 200, for example. The dielectric composition300 firstly comprises sintered particles and a grain boundary 10. Thesintered particles are categorized as sintered particles 20 notincluding a high-Bi phase, sintered particles 30 including a high-Biphase, and sintered particles 40 comprising only a high-Bi phase. Here,the sintered particles 30 including a high-Bi phase comprise a firstphase 8 comprising a high-Bi phase, and a second phase 9 comprising aportion within the sintered particles outside the high-Bi phase. Thehigh-Bi phase refers to a phase having a Bi concentration of at least1.2 times the mean Bi concentration of the dielectric composition as awhole.

There is no limit as to the number of first phases 8 included in thesintered particles 30 including a high-Bi phase. There is often only asingle first phase 8 included in a single sintered particle 30, but twoor more first phases 8 may equally be included. It should be noted thatthere is no particular limitation as to whether the sintered particles30 including a high-Bi phase are sintered particles in which the firstphase 8 is completely surrounded by the second phase 9 without makingcontact with the grain boundary 10, or sintered particles in which partof the first phase 8 is in contact with the grain boundary 10 and isincompletely surrounded by the second phase 9.

It should be noted that it is possible to appropriately control theamount of formation of the sintered particles 30 including a high-Biphase and the sintered particles 40 comprising only a high-Bi phase bymeans of the make-up of the dielectric composition and the method forproducing same, and also the baking conditions etc. For example, ifparticles having a large particle size are used in a starting materialpowder, the sintered particles 30 including a high-Bi phase and thesintered particles 40 comprising only a high-Bi phase tend to be readilyformed, while if the baking temperature is increased, the sinteredparticles 30 including a high-Bi phase and the sintered particles 40comprising only a high-Bi phase tend not to be readily formed.

There is no particular limitation as to the method for distinguishingthe sintered particles and the grain boundary 10, or to the method fordistinguishing the first phase 8 and the second phase 9. For example, itis possible to distinguish the sintered particles and the grain boundary10 by observing a cross section of the sintered dielectric composition300 by means of scanning transmission electron microscopy (STEM).Furthermore, it is possible to distinguish the first phase 8 and thesecond phase 9 by means of analysis using energy dispersive X-rayspectroscopy (EDS). Furthermore, the second phase 9 contains at leastNa, Bi and Ti.

Here, the dielectric composition 300 according to this embodiment issuch that the total surface area of the high-Bi phase (first phase 8)included in the sintered particles 30 including a high-Bi phase and thesintered particles 40 comprising only a high-Bi phase is between 0.1%and 15% with respect to the surface area of all the sintered particles.If the surface area of the first phase 8 is excessively small, theretends to be a deterioration in the dielectric constant when a DC bias isapplied (to be described later). If the surface area of the first phase8 is excessively large, there tends to be a deterioration in themechanical strength. It should be noted that the surface area of all thesintered particles refers to the surface area excluding the grainboundary 10. However, in actual fact the surface area of the grainboundary 10 is often small enough in comparison to the surface area ofall the particles that it can be ignored, so the surface area of theobservation field as a whole (the surface area of the dielectriccomposition 300 as a whole) is often deemed to be the surface area ofall the particles.

This embodiment is advantageous in that it makes it possible to obtain adielectric composition for which the dielectric constant when a DC biasis applied, the DC bias characteristics, the high-temperature loadlifespan and the mechanical strength are all favourable. It should benoted that the high-temperature load lifespan is sometimes also referredto as the “mean time to failure” (MTTF). Furthermore, there is noparticular limitation as to the method for determining the mechanicalstrength, and a method in which the transverse rupture strength ismeasured may be used, for example.

In addition, the dielectric composition is preferably such that1.15≤β≤2.15, where β is the total content of Bi atoms included in thefirst phase 8 with respect to the total content of Bi atoms included inthe second phase 9 (total content of Bi atoms in the high-Bi phaseincluded in the sintered particles/total content of the Bi atoms outsidethe high-Bi phase included in the sintered particles). When β is in theabovementioned range, the dielectric constant when a DC bias is appliedand the mechanical strength tend to be improved. An example of a methodfor measuring β will be described below. It should be noted that thereis no particular limitation as to the method for measuring β.

The composition of each first phase 8 in the sintered particlesdistinguished by STEM and EDS was analysed, preferably at 10 points ormore, and the mean value of the Bi concentration (atomic concentration)at each point was calculated. The Bi content of the first phase 8 wasobtained by multiplying the surface area of the first phase 8 by saidmean value. The composition of each second phase 9 was analysed in thesame way, preferably at 10 points or more, and the mean value of the Biconcentration (atomic concentration) at each measurement point wascalculated. The Bi content of the second phase 9 was obtained bymultiplying the surface area of the second phase 9 by said mean value.

Preferably, β can be calculated by taking at least 100 sinteredparticles and calculating the total of the Bi content of the first phase8 present in the sintered particles and the total of the Bi content inthe second phase 9 present in the sintered particles.

The high-Bi phase may be included anywhere in the dielectriccomposition, or the high-Bi phase may be included at the grain boundary10.

The sintered particles 20 not including a high-Bi phase and the sinteredparticles 40 comprising only a high-Bi phase may not be apparent in theabovementioned cross section or they may equally be entirely absent fromthe dielectric composition 300.

It should be noted that the auxiliary component may be present in any ofthe first phase 8, second phase 9 and grain boundary 10.

An example of a method for producing the laminated ceramic capacitorshown in FIG. 2 will be described below.

There is no particular limitation as to the method for producing thelaminated ceramic capacitor according to the present invention. Forexample, it is produced in the same way as a conventional laminatedceramic capacitor, namely by preparing a green chip using a normal sheetmethod or printing method employing a paste, baking the green chip andthen printing or transcribing external electrodes and then baking. Themethod for producing the laminated ceramic capacitor will be describedin specific terms below.

There is no particular limitation as to the type of paste for thedielectric ceramic layers. For example, said paste may be an organicpaint comprising a mixture of a dielectric starting material and anorganic vehicle, or it may be an aqueous paint comprising a mixture of adielectric starting material and an aqueous vehicle.

For the dielectric starting material, it is possible to use a metalcontained in the abovementioned dielectric composition, for example, anoxide of a metal selected from the group consisting of Bi, Na, Sr, Ti,La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Yb, Ba, Ca, Mg, and Zn, or amixture thereof, or a composite oxide may be used. In addition, thedielectric starting material may be appropriately selected from varioustypes of compounds which form the abovementioned oxides or compositeoxides as a result of baking, e.g., carbonates, oxalates, nitrates,hydroxides and organometallic compounds etc. and these may be mixed foruse.

When the paste for the dielectric layers is an organic paint, thedielectric starting material and an organic vehicle in which a binder orthe like is dissolved in an organic solvent should be mixed. There is noparticular limitation as to the binder which is used in the organicvehicle, and it may be appropriately selected from various conventionalbinders such as ethyl cellulose and polyvinyl butyral. Furthermore,there is no particular limitation as to the organic solvent which isused in the organic vehicle, and it may be appropriately selected fromvarious types of organic solvents such as terpineol, butyl carbitol,acetone and toluene, in accordance with the method which is used, namelythe printing method or sheet method etc.

Furthermore, when the paste for the dielectric layers is an aqueouspaint, the dielectric starting material and an aqueous vehicle in whicha water-soluble binder and a dispersant etc. are dissolved in watershould be mixed. There is no particular limitation as to thewater-soluble binder which is used in the aqueous vehicle, and saidwater-soluble binder may be appropriately selected from various types ofbinders such as polyvinyl alcohol, cellulose and water-soluble acrylicresin.

The paste for the internal electrode layers is prepared by mixing aconductive material comprising metals such as Au, Pt, Ag, Ag—Pd alloy,Cu or Ni, or various types of oxide which form the conductive materialafter baking, organometallic compounds, resinates, and the like, withthe abovementioned organic vehicle or aqueous vehicle. The paste for theexternal electrodes may be prepared in the same way as the paste for theinternal electrode layers.

When an organic vehicle is used to prepare the abovementioned pastes,there is no particular limitation as to the content of said organicvehicle. For example, the binder may be present in an amount of theorder of 1-5 wt % and the organic solvent may be present in an amount ofthe order of 10-50 wt %. Furthermore, the pastes may contain additivesselected from various types of dispersants, plasticizers, dielectrics,and insulators etc., as required. The total content of these additivesis preferably no greater than 10 wt %.

When a printing method is used, the paste for the dielectric layers andthe paste for the internal electrode layers are printed in layers on asubstrate made of polyethylene terephthalate (PET) or the like and cutto a predetermined shape, after which they are peeled from the substrateto form a green chip. Furthermore, when the sheet method is used, agreen sheet is formed using the paste for the dielectric layers, and thepaste for the internal electrode layers is printed on the green sheet,after which the green sheets are stacked to form a green chip.

Before the green chip is baked, a debinding treatment is performed.There is no particular limitation as to the conditions of the debindingtreatment and it should be carried out under normal conditions.

The debinding treatment is preferably carried out under a reducingatmosphere when a base metal alone or an alloy comprising a base metal,such as Cu or Cu alloy, is used for the conductive material of theinternal electrode layers. There is no particular limitation as to thetype of reducing atmosphere, and it is possible to use humidified N₂ gasor a mixed gas comprising humidified N₂ and H₂, among others.

There is no particular limitation as to the temperature increase rate,holding temperature and temperature holding time in the debindingtreatment. The temperature increase rate is preferably 0.1-100° C./hrand more preferably 1-10° C./hr. The holding temperature is preferably200-500° C. and more preferably 300-450° C. The temperature holding timeis preferably 1-48 hours and more preferably 2-24 hours. The organiccomponent such as the binder component is preferably removed down toaround 300 ppm by means of the debinding treatment, and more preferablyremoved down to around 200 ppm.

The atmosphere when the green chip is baked to obtain the capacitorelement main body should be appropriately determined in accordance withthe type of conductive material in the paste for the internal electrodelayers.

When a base metal alone or an alloy comprising a base metal, such as Cuor Cu alloy, is used as the conductive material in the paste for theinternal electrode layers, the oxygen partial pressure in the bakingatmosphere is preferably set at 10⁻⁶ to 10⁻⁸ atm. By setting the oxygenpartial pressure at 10⁻⁸ atm or greater, it is possible to restrictdegradation of the components forming the dielectric layers and torestrict a reduction in the resistivity. Furthermore, by setting theoxygen partial pressure at 10⁻⁶ atm or less, it is possible to restrictoxidation of the internal electrode layers.

Furthermore, the holding temperature during baking is 900-1400° C.,preferably 900-1100° C., and more preferably 950-1050° C. By setting theholding temperature at 900° C. or greater, this makes densification morelikely to progress adequately due to baking. Furthermore, when theholding temperature is set at 1100° C. or less, this facilitatessuppressing diffusion of the various materials forming the internalelectrode layers and abnormal sintering of the internal electrodelayers. By suppressing abnormal sintering of the internal electrodelayers, this facilitates preventing breakage of the internal electrodes.By suppressing diffusion of the various materials forming the internalelectrode layers, this facilitates preventing deterioration of the DCbias characteristics.

Furthermore, there is no particular limitation as to the bakingatmosphere. The baking atmosphere is preferably a reducing atmosphere soas to restrict oxidation of the internal electrode layers. There is noparticular limitation as to the atmospheric gas. A mixed gas comprisingN₂ and H₂ which is humidified is preferably used as the atmospheric gas,for example. Furthermore, there is no particular limitation as to thebaking time.

Annealing (reoxidation) may be carried out after the baking during theproduction of the laminated ceramic capacitor according to thisembodiment, but an atmosphere in which the dielectric layers areoxidized and the internal electrode layers are not oxidized ispreferred. Humidified N₂ gas or a mixed gas comprising humidified N₂ andH₂ etc. may be used, for example.

A wetter or the like should be used in order to humidify the N₂ gas orthe mixed gas comprising N₂ and H₂ etc. in the abovementioned debindingtreatment, baking and annealing. In this case, the water temperature ispreferably around 20-90° C.

The debinding treatment, baking and annealing may be carried outsuccessively or independently. When these processes are performedsuccessively, the following procedure is preferred, namely that thedebinding treatment is performed, after which the atmosphere is modifiedwithout cooling and then baking is carried out by raising thetemperature to the holding temperature for baking. On the other hand,when these processes are performed independently, the followingprocedure is preferred, namely that during baking the temperature israised under an N₂ gas atmosphere to the holding temperature for thedebinding treatment, after which the atmosphere is modified andtemperature increase is further continued, and then after baking coolingis performed to the holding temperature for the debinding treatment,after which the atmosphere is once again modified to an N₂ gasatmosphere and cooling is further continued. It should be noted that theabovementioned N₂ gas may or may not be humidified.

The end surfaces of the capacitor element main body obtained in this wayare polished by means of barrel polishing or sandblasting, for example,the paste for the external electrodes is printed or transcribed thereon,baking is carried out and the external electrodes are formed. The pastefor the external electrodes is preferably baked at 600-800° C. foraround 10 minutes to 1 hour under a humidified mixed gas comprising N₂and H₂, for example. A coating layer is then formed by means of platingor the like on the external electrode surface, as required.

Furthermore, the ceramic capacitor 100 shown in FIG. 1 can be producedusing a conventional method for producing a ceramic capacitor.

A ceramic capacitor and a laminated ceramic capacitor according to anembodiment of the present invention were described above. The dielectriccomposition according to the present invention simultaneously has a highdielectric constant when a high DC bias is applied, and also has good DCbias characteristics, high reliability and high mechanical strength, sosaid dielectric composition can be advantageously used for medium- andhigh-voltage capacitors with a relatively high rated voltage, forexample.

Furthermore, the present invention is not limited to the abovementionedembodiments. For example, the dielectric layer comprising the dielectriccomposition according to the present invention may also be used as adielectric element or the like in a semiconductor device. Furthermore,according to the present invention, a conventional configuration may befreely used, apart from the make-up of the dielectric composition.Furthermore, the calcined powder may be produced by means of a knownmethod such as hydrothermal synthesis when the ceramic capacitor isproduced, for example.

The dielectric element, electronic component and laminated electroniccomponent according to the present invention are advantageously used ina location where a relatively high rated voltage is applied. Forexample, they may be advantageously used in a power supply circuithaving a high rated voltage, such as in a DC-DC converter or an AC-DCinverter, for example.

The present invention makes it possible to provide a dielectriccomposition simultaneously having a dielectric constant of 1000 orgreater when a DC bias of 5 kV/mm is applied, DC bias characteristics of−20% to +20%, a high-temperature load lifespan of 20 hours or greaterwhen a DC voltage of 50 V/μm is applied at 150° C., and a transverserupture strength of 160 MPa or greater, and also a dielectric elementcomprising said dielectric composition, an electronic component and alaminated electronic component.

In addition, the dielectric element, electronic component and laminatedelectronic component according to the present invention are also of usein a smoothing capacitor or a snubber capacitor for circuit protectionfor which there is a need for a high dielectric constant when a high DCbias is applied.

In addition, the dielectric composition according to the presentinvention does not contain lead. The inventive dielectric composition,dielectric element, electronic component and laminated electroniccomponent are therefore also superior from an environmental point ofview.

The present invention will be described below in further detail with theaid of exemplary embodiments and comparative examples. However, thepresent invention is not limited by the following exemplary embodiments.It should be noted that the DC field applied to the dielectriccomposition, dielectric element, electronic component and laminatedelectronic component is referred to as a DC (direct current) bias.Furthermore, application of the DC bias causes a change in thedielectric constant and capacitance of the dielectric composition etc.,and the rate of change in the dielectric constant and the capacitancebefore and after application of the DC bias is referred to as the DCbias characteristics.

Exemplary Embodiments 1-18 and Comparative Examples 1-3

The following were prepared as starting materials: bismuth oxide(Bi₂O₃), sodium carbonate (Na₂CO₃), strontium carbonate (SrCO₃), bariumcarbonate (BaCO₃), calcium carbonate (CaCO₃), magnesium carbonate(MgCO₃), zinc oxide (ZnO), lanthanum hydroxide (La(OH)₃), neodymiumoxide (Nd₂O₃), samarium oxide (Sm₂O₃), gadolinium oxide (Gd₂O₃) andtitanium oxide (TiO₂).

The abovementioned starting material powders were weighed out in such away that the baked dielectric compositions had the make-up shown intable 1.

The weighed starting material powders were then wet-mixed using a ballmill, after which the resulting mixtures were calcined for 2 hours underthe air at 750° C.-850° C. to obtain calcined material. The resultingcalcined material was then wet-ground using a ball mill to obtaincalcined powders.

An organic solvent and an organic vehicle were then added to thecalcined powders, the material was wet-mixed using a ball mill and pastefor dielectric layers was prepared. At the same time, Ag powder, Ag—Pdalloy powder or Cu powder was mixed with an organic vehicle as aconductive material powder, and various pastes for internal electrodelayers comprising Ag, Ag—Pd alloy or Cu were prepared. The paste fordielectric layers was then moulded into sheets by means of asheet-moulding method.

The paste for the internal electrode layers was coated on the ceramicgreen sheets by means of screen printing to print the internal electrodelayers. The ceramic green sheets on which the internal electrode layershad been printed were then stacked, after which they were cut intoblocks, whereby laminated green chips were prepared. The laminated greenchips were subjected to debinding at 300° C.-500° C. to remove theorganic component down to around 300 ppm. After the debinding, bakingwas carried out under the atmosphere or under a reducing atmosphere at abaking temperature of 900-1400° C. The baking time was varied asappropriate. A mixed gas comprising humidified N₂ and H₂ was used as theatmospheric gas when baking was carried out under a reducing atmosphere.

After the baking, the exposed surfaces of the internal electrodes of theresulting laminated ceramic baked articles were polished, a paste forthe external electrodes having Ag or Cu as a conductive material wasapplied thereto, and laminated ceramic capacitors were obtained.

The size of the resulting laminated ceramic capacitors was 3.2 mm×1.6mm×0.6 mm, the thickness of the dielectric layers was 20 μm, and thethickness of the internal electrode layers was 1.5 μm. Four dielectriclayers were interposed between the internal electrode layers.

Auxiliary Component Content and Molar Ratio α of Bi with Respect to Sr

It should be noted that when the dielectric layers of the laminatedceramic baked articles were dissolved by means of a solvent and analysedby means of ICP optical emission spectroscopy, it was confirmed that thecomposition of the dielectric layers such as the auxiliary componentcontent and molar ratio α of Sr with respect to Bi was the same as inthe compositions shown in table 1.

A cross section at the intersection of the internal electrodes was cutfrom the laminated ceramic capacitors obtained and the crystal structureof the dielectric layers at that cross section was measured and analysedby means of X-ray diffraction (Rigaku Corporation; RINT-2500). As aresult, it was confirmed that the dielectric layers had a perovskitecrystal structure in all of the exemplary embodiments and comparativeexamples.

The abovementioned cross sections were then cut into flakes by means ofa gallium ion beam to prepare samples for cross-sectional observation.

The resulting samples for cross-sectional observation and the particlespresent in those cross sections were observed by means of scanningtransmission electron microscopy (STEM; JEM-2100F; JEOL). It should benoted that the observation field was 5 μm×5 μm and the magnification was40 000 times. Furthermore, a plurality of observation fields were set insuch a way that it was possible to select from the plurality ofobservation fields 100 particles for which it could be confirmed thatthe whole of each particle was surrounded by a grain boundary.

In addition, element mapping was performed by means of energy dispersiveX-ray spectroscopy (EDS) in the same observation fields and the X-rayspectrum of elemental Bi was measured. The mean concentration ofelemental Bi contained in the whole observation field was calculatedfrom the resulting X-ray spectrum. The elemental Bi mapping image wasthen subjected to image processing in such a way as to distinguish thephase in which the concentration of elemental Bi was at least 1.2 timesthe mean concentration (high-Bi phase), and the other phase. The high-Biphase present within the particles was the first phase, and the portionwithin the particles outside the high-Bi phase was the second phase.

Total Surface Area of High-Bi Phase with Respect to Total Surface Areaof Particles

S1+S2=S3 was established in the 100 particles, where S1 is the surfacearea occupied by the high-Bi phase (first phase), S2 is the surface areaoccupied by the portion outside the high-Bi phase (second phase), and S3is the surface area of the whole particle. S1, S2 and S3 were calculatedby selecting the respective regions, counting the number of pixelsoccupying each region, and multiplying the result by the surface areaper pixel. The proportion (%) of the surface area S1 of the high-Biphase with respect to the surface area S3 of the whole particle wascalculated by means of the following formula (1).

(S1/S3)×100  Formula (1)

It should be noted that in the exemplary embodiments, the experimentalresults for the abovementioned 100 particles were deemed to be equal tothe experimental results for the dielectric composition as a whole.

Total Bi Content β Included in the First Phase

The composition of the first phase included in the abovementioned 100particles was analysed. 10 or more measurement points were set for asingle first phase. The Bi content included in the first phase wascalculated by multiplying the mean value of the Bi concentration (atomicconcentration) at the measurement points in the single first phase bythe surface area of said single first phase in which the measurementpoints were included. The Bi content was then calculated for each firstphase included in the abovementioned 100 particles and the Bi contentsof the first phases were added together in order to calculate the totalBi content included in the first phase.

Meanwhile, the composition of the second phase included in theabovementioned 100 particles was analysed. 10 or more measurement pointswere set for a single second phase. The Bi content included in thesecond phase was calculated by multiplying the mean value of the Biconcentration (atomic concentration) at the measurement points in thesingle second phase by the surface area of said single second phase inwhich the measurement points were included. The Bi content was thencalculated for each second phase included in the abovementioned 100particles and the Bi contents of the second phases were added togetherin order to calculate the total Bi content included in the second phase.

The total Bi content of the first phase with respect to the total Bicontent of the second phase (β) was then calculated.

Dielectric Constant ε1

The dielectric constant ε1 (no units) of the laminated ceramic capacitorobtained was calculated from the capacitance measured from conditions ofroom temperature at 25° C., frequency 1 kHz, input signal level(measurement voltage) 1.0 Vrms, and distance between electrodes of thelaminated ceramic capacitor and effective surface area of theelectrodes, using a digital LCR meter (Hewlett-Packard; 4284A).

Dielectric Constant ε2

The dielectric constant ε2 (no units) was calculated from thecapacitance measured from conditions of room temperature at 25° C.,frequency 1 kHz, and input signal level (measurement voltage) 1.0 Vrms,effective surface area of the electrodes and distance betweenelectrodes, while a DC bias generator (GLASSMAN HIGH VOLTAGE; WX10P90)was connected to a digital LCR meter (Hewlett-Packard; 4284A) and a DCbias of 5 V/μm was applied to evaluation samples. A higher value for thedielectric constant ε2 is preferable, and a value of 1000 or greater wasdeemed to be good and a value of 1300 or greater was deemed to be evenbetter in the present exemplary embodiments.

DC Bias Characteristics

The DC bias characteristics were calculated by means of the followingformula (2) using the dielectric constant ε1 and the dielectric constantε2. A smaller absolute value for the DC bias characteristics ispreferable, and a value of −20% to +20% was deemed to be good and avalue of −15% to +15% was deemed to be even better in the presentexemplary embodiments.

DC bias characteristics (%)=100×(ε2−ε1)/1  Formula (2)

High-Temperature Load Lifespan

The high-temperature load lifespan was evaluated using a thermostaticbath and a digital ultra-high resistance meter (ADVANTEST; R8340A), bymaintaining a state of DC voltage application under an electric field of50 V/μm at 150° C. and measuring the lifetime. In the present exemplaryembodiments, the lifespan was defined as the time from the start ofapplication until the insulation resistance fell to a single digit.Furthermore, this evaluation was carried out for 10 capacitor samplesand the mean value thereof was taken as the high-temperature loadlifespan. A value of 20 hours or greater was deemed to be good and avalue of 25 hours or greater was deemed to be even better in the presentexemplary embodiments.

Transverse Rupture Strength

The method for measuring the transverse rupture strength will bedescribed in detail below.

1 part by weight of polyvinyl alcohol (PVA) was added to 100 parts byweight of calcined powder, the resulting material was moulded under apressure of 196-490 MPa and square plate-shaped moulded articles havingplanar dimensions of the order of length 20 mm, width 20 mm andthickness 1 mm were obtained.

The resulting square plate-shaped moulded articles were baked under theair at a baking temperature of 900-1100° C. for a baking time of 2-10hours in order to obtain sintered compact samples. When the density ofthe resulting sintered compact samples was measured, it was found thatthe density of all of the samples was 95% or greater with respect to thetheoretical density.

The sintered compact samples obtained were processed to a length of 7.2mm, a width of 2.5 mm and a thickness of 0.32 mm using a double-sidedlapping machine and a dicing saw, and 20 samples for transverse rupturestrength measurement were obtained for each sample. The maximum load (N)when the samples for transverse rupture strength measurement were brokenby three-point bending by means of machine model 5543 produced byINSTRON with a distance between support points of 5 mm was measured foreach of the 20 samples and the transverse rupture strength wascalculated. A higher transverse rupture strength is preferable, and avalue of 160 MPa or greater was deemed to be good and a value of 170 MPaor greater was deemed to be even better in the present exemplaryembodiments.

TABLE 1 High- Auxiliary (Bi in first DC bias temperature componentSurface area of first phase)/ characteristics load Transverse Molarratio Amount phase with respect (Bi in Dielectric Dielectric (%),lifespan (h) rupture α of Bi with (molar to surface area of secondconstant constant application of 150° C.-50 V/ strength Sample no.respect to Sr Type parts) particle as a whole phase) β ε1 ε2 5 V/μm μm(MPa) Exemplary 0.17 La 3.3 0.1 2.40 1150 1090 −5.2 33 275 Embodiment 1Exemplary 0.23 La 3.3 0.8 2.15 1430 1332 −6.9 31 270 Embodiment 2Exemplary 0.33 La 3.3 1.8 1.97 2022 1859 −8.1 30 274 Embodiment 3Exemplary 0.50 La 3.3 3.0 1.90 2448 2307 −5.8 30 261 Embodiment 4Exemplary 0.69 La 3.3 4.9 1.50 2234 2016 −9.8 28 232 Embodiment 5Exemplary 1.08 La 3.3 6.1 1.44 2263 2076 −8.3 27 215 Embodiment 6Exemplary 1.17 La 3.3 8.5 1.30 2263 2300 1.6 26 177 Embodiment 7Exemplary 2.00 La 3.3 9.4 1.24 1783 1895 6.3 26 175 Embodiment 8Exemplary 2.47 La 3.3 13.2 1.15 1717 1720 0.2 25 173 Embodiment 9Exemplary 2.83 La 3.3 15.0 1.10 1607 1615 0.5 21 166 Embodiment 10Exemplary 0.50 Nd 3.3 4.2 1.86 2280 2165 −5.0 31 238 Embodiment 11Exemplary 0.50 Sm 3.3 4.0 1.73 2125 2040 −4.0 32 240 Embodiment 12Exemplary 0.50 Gd 3.3 3.3 1.79 2240 2065 −7.8 32 250 Embodiment 13Exemplary 0.52 Mg 0.5 3.6 1.05 3456 2840 −17.8 22 264 Embodiment 14Exemplary 0.72 Mg 5.3 5.5 1.53 2374 2664 12.2 31 230 Embodiment 15Exemplary 2.00 Mg 11.1 9.0 1.10 1796 1817 1.2 22 210 Embodiment 16Exemplary 0.72 Zn 5.3 5.8 1.34 2118 1854 −12.5 31 263 Embodiment 17Exemplary 0.63 Ca 10.0 6.0 1.30 1880 1608 −14.5 30 215 Embodiment 18Comparative 0.13 La 3.3 0.0 2.62 1025 950 −7.3 37 289 Example 1Comparative 0.50 None 0.0 8.7 1.23 4666 2414 −48.3 22 163 Example 2Comparative 4.50 None 0.0 17.0 1.02 1027 502 −51.1 12 140 Example 3

It can be seen from the above that the dielectric compositions accordingto Exemplary Embodiments 1-18 include particles having a perovskitecrystal structure including at least Bi, Na, Sr and Ti. Furthermore, themolar ratio α of Bi with respect to Sr satisfies 0.17≤α≤2.83. Inaddition, the auxiliary component is included in an amount of between0.5 molar parts and 11.1 molar parts, taking the Ti content of thedielectric composition as 100 molar parts. Furthermore, at least some ofthe particles comprise a high-Bi phase having a Bi concentration of atleast 1.2 times the mean Bi concentration of the dielectric compositionas a whole. In addition, the total of the surface area of the high-Biphase satisfies a value between 0.1% and 15% of the total surface areaof the particles as a whole. The dielectric compositions according toExemplary Embodiments 1-18 demonstrated a dielectric constant ε2 when aDC bias of 5 V/μm was applied of 1000 or greater, DC biascharacteristics of −20% to +20%, a high-temperature load lifespan at 50V/μm under a temperature of 150° C. of 20 hours or greater, and atransverse rupture strength of 160 MPa or greater.

Furthermore, the dielectric compositions according to ExemplaryEmbodiments 2-9, 11-13, 15 and 17-18, in which the total amount of Biincluded in the first phase is, as an atomic ratio, between 1.15 timesand 2.15 times the total amount of Bi included in the second phase(1.15≤β≤2.15) demonstrated a dielectric constant ε2 when a DC bias of 5V/μm was applied of 1300 or greater, DC bias characteristics within±15%, a high-temperature load lifespan at 50 V/μm under a temperature of150° C. of 25 hours or greater, and a transverse rupture strength of 170MPa or greater.

In contrast to this, the dielectric compositions according toComparative Examples 1-3 in which α<0.12 or α>1.99, the auxiliarycomponent content is less than 0.5 molar parts or greater than 11.1molar parts, or the total surface area of the high-Bi phase is less than0.1% or greater than 15% with respect to the total surface area of theparticles as a whole demonstrated a dielectric constant ε2 when a DCbias of 5 V/μm was applied of less than 1000, DC bias characteristicsoutside the range of −20% to +20%, a high-temperature load lifespan at50 V/μm under a temperature of 150° C. of less than 20 hours, or atransverse rupture strength of less than 160 MPa.

1. Dielectric composition comprising particles having a perovskitecrystal structure including at least Bi, Na, Sr and Ti, characterized inthat: said dielectric composition includes at least one selected fromamong La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Yb, Ba, Ca, Mg and Zn; thecontent of the at least one selected from among La, Ce, Pr, Nd, Sm, Eu,Gd, Tb, Dy, Ho, Yb, Ba, Ca, Mg and Zn is between 0.5 molar parts and11.1 molar parts, taking the Ti content of the dielectric composition as100 molar parts; 0.17≤α≤2.83, where α is the molar ratio of Bi withrespect to Sr in the dielectric composition; at least some of theparticles include a high-Bi phase having a Bi concentration of at least1.2 times the mean Bi concentration of the dielectric composition as awhole; and the total surface area of the high-Bi phase within theparticles in the cross section of the dielectric composition is between0.1% and 15% of the total surface area of the particles. 2-5. (canceled)